1. Field of the Invention
The present invention relates to a filter cartridge for cleaning the dedusting filter of a silo. Cleaning is effected by air blown intermittently into the filter cartridge and introduced through an air nozzle disposed above the filter cartridge.
A dedusting filter of this kind is used for filtering the outgoing air during pneumatic filling of a silo with pulverulent bulk material, such as for example cement. During the filling operation the air used as carrier medium for the filling flows, together with the filling material, from the outside against the filter surface forming a filter jacket of the filter. Since only the air can escape through the filter to the atmosphere, the filling material is deposited on the outside of the filter surface. To prevent the filter from becoming ineffective, it must be cleaned from time to time.
2. The Prior Art
It is known to clean the filter by intermittently blowing compressed air from above into its interior. During this cleaning operation the filter cannot perform its filtration function, since during this period no air can flow through its filter jacket from outside to inside.
In order to ensure that during the cleaning operation, in the course of which the pressure inside the filter is raised by the compressed air blown in, the pressure relief valve on the silo will not open with the consequence that filling material will be blown out of the silo through this forced venting, which is highly undesirable both for reasons of economy and, in particular, because of the consequent pollution of the environment, it is known from WO 87/02268 to dispose a plurality of filter cartridges inside a filter and to clean them in turn at intervals so timed that the filter cartridges are never all cleaned at the same time and thus made unavailable for the filtering operation. The air nozzles allocated to the various filter cartridges are controllably connected to an additionally provided air reservoir in such a manner that after a cleaning cycle, which is brought into action through the existence of a determined superatmospheric pressure in the filter, at least one further cleaning cycle can take place. It is thus ensured that on completion of a filling operation the filter tubes will be in a clean condition.
The smaller the filter cartridge, the easier it is--that is to say the smaller the amount of air required--to produce superatmospheric pressure in the filter cartridge for cleaning purposes. Filter cartridges of the smallest possible diameter are therefore desirable from the point of view of cleaning. On the other hand, the filter action depends on the size of the filter jacket. However, the fewer the filter cartridges used to provide a determined total filter jacket surface, the lower the overall cost of the filter will be. A smaller number of filter cartridges for a comparable filter surface will of course necessitate filter cartridges of a larger diameter. The size of the diameter of a filter cartridge is of practically no importance where the filtering operation is concerned, but on the other hand a larger filter cartridge diameter has a detrimental effect on cleaning, since the nozzle disposed about the filter cartridge must be designed for a corresponding high air delivery.
A filter cartridge of the type first mentioned above is known from EP-A 0 225 445. A rod, which is surrounded by a jacket of circular annular cross section, projects centrally through the filter cartridge of circular cross section which is disclosed therein. Between this jacket and the filter longitudinally extending partitions are provided, which subdivide the interior of the filter cartridge into a plurality of interior regions. Above each of these interior regions is disposed an air nozzle through which compressed air can be blown into the interior of the respective interior region. The compressed air required for this purpose is supplied from outside to the filter cartridge by way of a pipe system.
In the filter cartridge known from EP-A 0 142 951 the interior space is likewise subdivided into a plurality of pocket-like interior regions by means of a plurality of partitions extending in the vertical direction. These interior regions can likewise be supplied with compressed air one after the other by means of respective air nozzles disposed above them. This compressed air is likewise supplied to the filter cartridge from outside.